It is customary in can assembly operations to dispense a sealant material into an annular groove of a can lid for sealed attachment of the lid to the open end of a can body. Typically, this is done through the use of a rotary can end lining machine in which the sealant dispensing nozzle is opened mechanically and thereafter closed automatically by a spring. A compound cam and linkage usually form the mechanism for opening the nozzle, and the spring will then close the nozzle by advancing a valve stem into the nozzle opening. The can lids are advanced in rapid succession onto continuously rotating chuck(s) and one or more sealant applicator nozzles must be activated over a predetermined period of time to deliver a selected amount of sealant compound onto the groove of each lid as it is advanced into alignment beneath a nozzle, then rotated beneath the nozzle to evenly apply the sealant into the groove of the lid, following which the lid is ejected from the table into a collection area. Accordingly, the application of sealant to each lid in the proper amount and over a predetermined time period is a very highspeed, precise operation, and the setting of the nozzle and associated linkage requires regular maintenance in order to keep the amount of sealant applied within acceptable limits. In the past, this maintenance involved a high degree of skill and considerable downtime of the machine when adjustment was required or any breakage occurred.
It is therefore highly desirable to provide for a sealant applicator which eliminates the mechanical opening and closing control mechanisms employed in the past including any of the linkage required by existing mechanical designs. More specifically, it is proposed to electrically control opening and closing of the valve stem used in association with the nozzle and wherein the electrical control system is mounted directly in line with the valve stem so as to eliminate any direct or offset linkage and consequent wear on pivot points. Further, it is important to be able to adjustably control the amount of sealant applied to each can lid by closely coordinating the movement of the valve stem between the open and closed positions with the time interval established for application of the sealant.
The quality of sealant applied by each nozzle can be determined by pre-weighing and post-weighing each lid before and after the sealant is applied. In the mechanical systems previously employed, the stroke of the valve stem was adjusted to compensate for any changes in the weight or amount of sealant applied by each nozzle; however, the actual stroke was effected by the various linkage and tended to deteriorate with constant operation. As a result, it was necessary to stop the machine and make the necessary adjustments to control the stroke of the valve stem; and these adjustments would become more frequent as the linkage deteriorated. In accordance with the present invention, the stroke of the valve stem or needle is electrically activated and any adjustment required to the stroke is controlled by a stop member directly in line with the path of movement of the valve stem and which can be instantaneously adjusted to compensate for any changes in weight of the sealant applied to each nozzle without any downtime or interruption of the operation. Furthermore, the system of the present invention enables the opening time, duration of opening, closing and valve stroke to be controlled, adjusted and displayed on a screen so that the operator has complete control over each operation while the machine is running.